BOSTON -- .Mark Lawton, a retired judge, agreed he tried to “tilt the scales” for his son, and believed the young man’s prescription drug addiction was “under control” when he enlisted Senate President Therese Murray to help get the young man a probation officer job in 2008.

Patrick Lawton was one of the key hires that federal prosecutors are attempting to prove exemplified a patronage system that rewarded less qualified applicants with political backing under the cover of meaningless job interviews that made the process appear merit-based.

Former Probation Commissioner John O’Brien and two of his former deputies, Elizabeth Tavares and William Burke III, have pleaded not guilty and have attempted to show that patronage hiring has been a widely accepted practice in state government.

Patrick Lawton took the stand after his father Tuesday, telling the jury he first used heroin in 2009, after he was hired as a probation officer at a family court in Brockton.

A law school graduate who failed the bar exam three times, Patrick Lawton said he used marijuana, alcohol and pain medication on weekends while attending the New England School of Law. He first used cocaine in college, he said, saying his drug use then was limited to the weekends.

Federal prosecutor Fred Wyshak pressed the now 34-year-old man and his 64-year-old father about what they hoped to gain by working with Murray’s aide, Francine Gannon, who has said part of her job handling constituent services for the Senate president involves helping people find work in state government.

“I was just unemployed. I was just a poor kid looking for work,” Patrick Lawton said, explaining how his then fiancée helped him find job openings after he was laid off as a WB Mason salesman. Patrick Lawton listed as references Norfolk Sheriff Michael Bellotti, a law school classmate; his fiancée’s mother; and a friend who served with him on the Zoning Board of Appeals in Bridgewater.

Mark Lawton said he did not tell O’Brien about his son’s drug use, and said the two would often see each other at track meets where their daughters competed, but their discussion there was limited to the running.

“I talked to Jack quite often when I would see him at track meets,” Mark Lawton said, prompting suppressed giggles from the front row where O’Brien’s family sits when he said the Quincy girls usually won.

Hoping to help with his son’s job search after Patrick Lawton was laid off by WB Mason, Mark Lawton reached out to Murray’s office and to then-Sen. Jack Hart, writing an email for his son to send to the former South Boston Democrat.

Page 2 of 4 - “I’ve lost a bit of sleep worrying about Patrick’s plight . . . It’s painful to watch,” Mark Lawton, who also served in the Massachusetts House, wrote in a March 2008 email to Hart.

The Lawtons are a prominent Brockton family who moved to Bridgewater.

“The way we were brought up, we thanked everybody, whether they helped or not,” said Mark Lawton. Asked why he wrote the letter to Hart for his son to send, he said, “I wanted to make sure it would get done.”

Hart is one of the upcoming witnesses for the prosecution, and he would be the first current or former lawmaker to testify in the corruption trial. Before Hart, the U.S. Attorney’s office expects Ed Driscoll, a regional supervisor for the probation department, will testify. Patrick Lawton has not yet concluded his testimony.

Evidence has shown Patrick Lawton was effusive in his praise of Gannon, leaving handwritten notes laden with exclamation marks. Like his father, Patrick Lawton was somewhat cagey under prosecution questioning about what he wanted Gannon to do and what he was so thankful for.

“You knew how the system worked,” Wyshak asserted with Mark Lawton on the stand. He said, “And you exploited it to your own and your son’s benefit.”

“I tried to,” said Mark Lawton, who also contacted a boyhood friend who grew up in similar circumstances in Brockton’s East Side, former Sen. Robert Creedon.

Patrick Lawton at first said he left a prior job as a Plymouth County assistant district attorney because he failed the bar, losing responsibilities, and he wanted “a more lucrative job.” Only later Patrick Lawton said a third issue was his main reason for leaving: a politically charged email he wrote on a work computer, which became a major news story covered by the Brockton Enterprise.

Patrick Lawton, who is now not married, said his then-fiancée who was a teacher helped him with the job search. A list sent to Gannon shows he was interested in working as deputy press secretary for the attorney general, an access specialist for the Office of Disability, an official within Elder Affairs and a program manager at the then Department of Social Services, in addition to a hearing officer position at the Registry of Motor Vehicles that was his first choice. The probation job was only penned in later.

Lawton said he was not using drugs at the time of a second-round interview for the probation job at Plymouth County Probate & Family Court, where two of his interviewers, Judge Catherine Sabaitis and then Chief Probation Officer Michael LaFrance, both testified he was sweating, trembling and nervous.

Page 3 of 4 - Under questioning from Wyshak, Mark Lawton acknowledged that his knowledge that his son wasn’t using drugs at the time of the interview was based on the fact that “we didn’t know otherwise.”

“His problem with addiction drugs we believed was under control,” said Mark Lawton, who described his son using prescription drugs to stay up studying at law school. He said, “It didn’t interfere with his everyday functioning.”

Patrick Lawton said he is now working as a teacher at the Brockton Champion High School, an alternative public school for students ages 16 to 21.

In contrast to many of the other witnesses testifying as unindicted co-conspirators, there was no questioning directed toward either of the Lawtons about any immunity deals or any designation as being part of the alleged conspiracy.

Mark Lawton claimed LaFrance had his own favored candidate, a “young woman,” and that was why Mark Lawton, then a judge, was trying to pull strings on his son’s behalf. Mark Lawton, who retired from the bench in July 2010 shortly after a Boston Globe expose into probation hiring, said he heard LaFrance “would do whatever he could to get her hired.”

Mark Lawton was later unable to tell Wyshak where he had heard that information about LaFrance, and acknowledged that he knew little about the other candidates. He also said he tried to use his influence to help his son at a variety of other jobs where he had no knowledge of anyone else trying to “skew” the process on behalf of someone else.

“You think there’s anything wrong with trying to help your son?” asked O’Brien’s defense attorney Stellio Sinnis. Mark Lawton agreed with Sinnis that recommendations can be part of a merit-based hiring process and also that “Recommendations are meant to tilt the scales.” Asked if he tried to “tilt the scales,” the retired judge said, “Partially.”

Mark Lawton, who was a state representative from 1975 into the start of 1983, said he had helped LaFrance get a job and helped Sabaitis become a judge.

Burke’s attorney John Amabile drew out of Mark Lawton that his son had lived his whole life in Brockton and Bridgewater, suiting him to work as a probation officer in the area. Under Amabile’s questioning, Mark Lawton agreed that references had been part of court hiring from the time when it was run by county government, through various reforms and it “continues right up until today.” Mark Lawton also said at a previous meeting that prosecutors falsely suggested he had known his son was an active drug user when he pushed him for a job, and suggested that he would “automatically” receive a job with the political backing.

Page 4 of 4 - Mark Lawton said that although he told Gannon in an email that “I know that Jack O’Brien takes very seriously calls from your office where there’s a strong interest on the part of the Senate President,” he had actually only assumed that.

“I knew nothing,” Mark Lawton said.

“We are all doing our best to have you among the ranks of the employed by your wedding in July!!!! I am also sorry to hear about your future bride being laid off from her job,” Gannon wrote in a May 31, 2008 email around the time Lawton was hired. Testifying with immunity, Gannon told the jury that helping people with jobs, immigration issues and unemployment insurance was rewarding work.

Judge William Young uniquely caters to the jury, allowing the 16 individuals to ask questions by writing, and while many jury questions in the trial have been largely technical or procedural in nature, questions asked Tuesday got at some fundamental issues, including the specifics and timing of Patrick Lawton’s drug use. Young asked Mark Lawton a question from the jury about how he would vet job applicants seeking his recommendation when he was a state representative.

“I could tell when I talked to someone whether or not they were qualified,” Mark Lawton said.